Epoxy resins are widely used in industrial fields of coating materials, adhesives, electric and electronic information materials, advanced composite materials and the like owing to their excellent mechanical properties. Epoxy resins are particularly heavily used in fiber reinforced materials made from a reinforcing fiber such as a carbon fiber, a glass fiber, and an aramid fiber, and a matrix resin.
As a method for producing the fiber reinforced material, an appropriate method is selected from methods such as a prepreg, method, hand lay-up, filament winding, pultrusion, and Resin Transfer Molding (RTM). Of these methods, the filament winding, pultrusion, and RTM in which a liquid resin is used are particularly actively applied to industrial applications such as pressure vessels, electric wires, and automobiles.
Generally, a fiber reinforced material produced by the prepreg method has excellent mechanical properties because the arrangement of the reinforcing fiber is precisely controlled. Meanwhile, with the recent growing interest in the environment and the trend toward greenhouse gas emission control, higher strength is required of fiber reinforced materials made from a liquid resin similarly to those produced by the prepreg method.
Patent Document 1 discloses a resin for RTM that contains an aliphatic amine hardener and an aromatic amine hardener in combination, rapidly cures at low temperatures, and is excellent in heat resistance. Patent Document 1 also discloses the use of 2,6-diethylaniline as the aromatic amine hardener.
Patent Document 2 discloses an epoxy resin composition that contains a specific bifunctional epoxy resin and a specific aromatic diamine hardener, and is capable of providing a fiber reinforced material excellent in heat resistance, compression strength, and toughness.
Patent Document 3 discloses a low-viscosity epoxy resin composition that contains two kinds of different hardeners and is excellent in produce ability.
Patent Document 4 discloses an epoxy resin composition that contains p-tert-butyl phenyl glycidyl ether as a reactive compound and is excellent in heat resistance and compression properties.
Patent Document 5 discloses an epoxy resin composition that is characterized in having a rubbery plateau portion modulus of 10 MPa or less, and capable of providing a prepreg excellent in adhesion to a honeycomb core and tensile strength.
Patent Document 6 discloses a resin composition that contains a resin composed of a tri- or tetrafunctional epoxy resin and hardeners different in reactivity, and is capable of improving produce ability and compression properties. Patent Document 6 also discloses the use of 4-aminodiphenylamine, which is an aromatic diamine, as a hardener.
Patent Document 7 discloses an epoxy resin composition for a tow prepreg that contains an acid anhydride as a hardener, and is excellent in heat resistance and fracture toughness.
Patent Document 8 discloses a low-viscosity epoxy resin composition that contains a polyfunctional epoxy resin excellent in heat resistance and an acid anhydride as a hardener, and is excellent in heat resistance and rapid-curing property.
Patent Document 9 discloses an epoxy resin composition for RTM that contains an alicyclic epoxy resin, and is excellent in the balance between strength and elongation.
Patent Document 10 discloses a resin for RTM that contains a substituted phenyl glycidyl ether, and is capable of providing a fiber reinforced material excellent in workability and mechanical strength.
Patent Document 11 discloses a resin composition that contains a monofunctional epoxy, in particular, glycidyl phthalimide, and a trifunctional or higher functional epoxy resin, and is capable of improving impact resistance and mechanical characteristics at low temperatures.
Patent Documents 12 and 13 disclose an epoxy resin composition for FRP that contains an epoxy having a pendant group or a monofunctional epoxy and a polyfunctional epoxy, and is excellent in heat resistance and strength properties.
Patent Document 14 discloses an epoxy resin composition that combines heat resistance with mechanical properties owing to incorporation of a thermoplastic resin.